The present invention relates to free-flow protection devices and methods for use with intravenous infusion pumps. The free-flow protection devices are operative in occluding a pumping tube to prevent free-flow of a medicant to a patient.
Intravenous infusion pumps are used to deliver a fluid which may include medicants or nutrients to a patient through a tube set. The tube set, commonly referred to as an administration set, typically includes a tube connected between a source of fluid and a tube which passes into the patient. Infusion pumps operate to either force fluid from the source through the tube and into the catheter or control the flow of fluid through the tube into the catheter. Infusion pumps may include peristaltic pumps, roller pumps or expulsor type pumps. Examples of infusion pumps are illustrated in U.S. Pat. No. 4,559,038 to Berg, U.S. Pat. No. 5,096,385 to Georgi and U.S. Pat. No. 4,394,862 to Shim.
These infusion pumps effect the movement of fluid through the tube by selectively occluding portions of the tube by depressing a valve or finger against the tube. For example, U.S. Pat. No. 5,056,385 to Georgi illustrates a peristaltic pump in which the tube is positioned between a plurality of fingers and a pressure plate. The source of fluid is positioned in a bag remote from the pump. The fingers of the pump selectively engage the tube against the pressure plate in a peristaltic fashion to force fluid through the tube. The fingers of the Shim patent may also be used to control the flow of fluid through the tube.
The pump disclosed in U.S. Pat. No. 4,559,038 is an expulsor pump which effects the delivery of fluid from a reservoir to the patient. In the '038 patent, the fluid is in a bag held in a container, or cassette, immediately adjacent to the pump. The pump effects the amount of fluid to the patient by physically occluding the tube against a pressure plate which restricts the volume of fluid allowed to flow to the patient. The pump includes a pump mechanism which engages the tube with an inlet valve, an outlet valve and a central expulsor which squeezes the tube against the pressure plate associated with the cassette to effect pumping of the fluid. The pump of the '038 patent has also been used with a pressure plate not having a self contained fluid reservoir, where the fluid is in a bag positioned remote from the pump.
Free-flow is the condition where fluid flows freely from the source of fluid through the t-be and into the patient. Caregivers attempt to avoid frees-flow when administering fluids with an infusion pump. Fluid flow may be a result of a pressure head associated with the administration set which is greater than the blood pressure of the patient. The free-flow condition will continue until the pressure head of the administration set equalizes with the blood pressure of the patient. A free-flow condition may cause significant harm to the patient including harm which is the direct result of over medicating the patient.
Typically, free-flow will not occur when the tube set is attached to the infusion pump because the roller, at least one valve, or finger of the infusion pump always occludes the tube at any given time. When the tube is engaged by the pump it is temporarily occluded and fluid will not flow. However, if the tube disengages from the pump, the tube will no longer be occluded by the pump and a free-flow condition may exist.
Free-flow can be prevented by providing a valve positioned in-line with the administration set. One such valve is described in U.S. Pat. No. 4,535,820 to Raines. Raines describes an in-line pressure valve which requires a predetermined crack pressure or differential pressure, such as 1.5 psi, to open the valve. In an administration tube set, the infusion pump will create a pressure increase within the tube above the crack pressure of the valve, thereby opening the valve and allowing fluid to be delivered to the patient.
However, the valve of Raines does not fully solve the problem of unwanted free-flow. For example, situations may exist when the pressure head provided by the source of fluid may be great enough to open the valve of Raines, resulting in unnecessarily delivering fluid to the patient. Further, the addition of the valve of Raines in an administration set may affect the volume of fluid delivered to a patient in a normal fluid delivery cycle. Because of these and other problems within the prior art a need has arisen to provide devices and methods which guarantee that free-flow will not occur when the tube becomes disengaged from the infusion pump.